1. Field of the Invention
The present invention relates, generally, to a method and apparatus for refurbishing a valve seat. More specifically, the present invention relates to a method and apparatus for refurbishing the valve seat associated with a valve bore extending through a fuel injector body.
2. Background Art
Fuel injector assemblies are employed in internal combustion engines for delivering a predetermined, metered mixture of fuel and air to the combustion chamber at preselected intervals. In the case of compression ignition, or diesel engines, the fuel/air mixture is delivered at relatively high pressures. Presently, conventional injectors deliver this mixture at pressures as high as 32,000 psi. These are fairly high pressures and have required considerable engineering attention to ensure the structural integrity of the injector, good sealing properties, and the effective atomization of the fuel within the combustion chamber. However, increasing demands on greater fuel economy, cleaner burning, fewer emissions and NOx control have placed, and will continue to place, even higher demands on the engine""s fuel delivery system, including increasing the fuel pressure within the injector. Fuel injectors presently employed in the related art typically include a high pressure fuel passage, which extends between a solenoid actuated control valve and the plunger cylinder in the injector body. Fuel at relatively low pressure is supplied to the control valve which then meters the delivery of the fuel at very high pressures and at predetermined intervals through the high pressure fuel passage to the plunger cylinder. The fuel ultimately exits the injector through a fuel nozzle.
The solenoid actuated control valve is supported in a stepped bore which typically extends through a side body of the injector. The stepped bore defines a supply chamber and a valve bore, which receives a valve stem of the associated control valve. The valve bore terminates in a chamfered valve seat which is formed so as to define an angle relative to the centerline of the valve bore. Similarly, the valve stem terminates in a head which seats against the valve seat under the force generated by the solenoid. The head is configured to mate closely with the valve seat.
At least a portion of the valve stem is subject to the high pressure generated in a valve opening direction during an injection cycle. Accordingly, the solenoid must generate sufficient force in the valve closing direction to overcome such pressure. These forces are borne by the valve seat through the head of the control valve. Fuel injectors and their associated sub-components must endure millions of injection cycles during a standard useful life of the injector. While individual components may wear out, the injector body, per se, having no moving parts, is capable of reuse. The injector body is an expensive part of the injector assembly. It includes many precisely machined ports, passageways, slots, and other surfaces. However, one barrier to the reuse of the injector body has been refurbishing the solenoid valve seat. The valve seat typically endures significant punishment over the useful life of the injector and must be machined to bring it back within specification. The concentricity of the valve seat about the centerline of the valve bore is an important parameter that must be precisely controlled during any refurbishing process. In the past, there has been a lack of methods and apparatuses that may be employed to quickly, effectively and efficiently refurbish the solenoid valve seat on a production basis. This fact has contributed to the tendency to scrap the injector body after the less durable sub-components have been spent.
Thus, there is a need in the art for a method and apparatus which may be employed to refurbish or recondition the solenoid valve seat on a production basis and thereby extend the useful life of the injector body.
The present invention overcomes the disadvantages in the related art in a method and apparatus of refurbishing a valve seat disposed at a predetermined angle relative to the centerline of an associated valve bore in a workpiece, such as an injector body. The method includes the steps of locating the workpiece in a predetermined position relative to a support structure such that the centerline of the valve bore is aligned with a known reference axis. A tool having a lapping portion corresponding to the valve seat is then moved along the known axis such that the lapping portion is brought into engagement with the valve seat. The tool is rotated relative to the workpiece to lap the valve seat and then moved along the known axis to disengage the lapping portion from the valve seat. Similarly, the apparatus of the present invention includes a support structure on which the workpiece is located such that the centerline of the valve bore is aligned with the known axis. The apparatus also includes a tool having a lapping portion corresponding to the valve seat and a drive mechanism for moving the tool along the known axis such that the lapping portion is brought into engagement with the valve seat. The drive mechanism also rotates the tool relative to the workpiece to lap the valve seat.
One advantage of the present invention is that a method and apparatus are provided which are adapted to quickly, efficiently and effectively refurbish a valve seat on an injector body on a production basis. Another advantage of the present invention is that the useful life of an injector body may be extended beyond the relatively short lives of certain injector sub-components. Still another advantage of the present invention is that the valve seat is refurbished while the concentricity of the valve seat about the centerline of the valve bore is closely controlled.